This article analyses the work of prevention within a specific social field: the families of prisoners. From this place of experience, it examines how prevention takes shape as a technology of government that guides practices, thoughts and ways of being. Within this relational movement, this article theorizes the concept of “subject of prevention” in order to explain how a framework of subjectivation emerges as an agent of moral discipline, which is conceived through a neoliberal grammar of state programs, translated into ordinary language by NGO workers and driven by the imperative to prevent.